Antifoam agents (also known as defoamers) are used as processing aids for foam control, improving filtration, dewatering, washing, and drainage. Antifoams find use in the pulp and paper industry, the paint and latex industry, the textile industry, the fermentation industry, and the detergent industry.
The components of an antifoam composition are generally divided into five functional classifications: primary antifoam agent, secondary antifoam agent, a carrier, an emulsifier, and a stabilizing agent. However, the functions of the components sometimes overlap each other so that fewer components may be required. The primary antifoaming agents comprise highly insoluble particulate materials such as hydrophobic silicas, fatty amides, and fatty acids or esters. They are in most cases insoluble in the carrier. Secondary antifoaming agents modify the crystallinity, surface properties, solubility and roughness of the primary antifoaming agents. The carriers comprise the bulk of the antifoam formulation and include hydrocarbon oils, silicone oils, or water. Emulsifiers help the active antifoam agents to spread over foams whereas stabilizing agents prolong the shelf life of the antifoams, and comprise preservatives or cosolvents for the carriers and the actives.
In practice, the principal ingredients for most antifoams are hydrophobic particles and hydrophobic oils such as hydrocarbon oils and silicone oils. A representative formulation for hydrocarbon-based antifoam consists of 4 parts of stearic diamide of ethylene diamine, 1 part of Castrol motor oil, 3.5 parts of vinyl acetate-fumaric acid copolymer, 91.3 parts of paraffin oil, and 0.2 parts of silicone oil. On the other hand, a representative formulation of silicone-based antifoam consists of 2.7 parts of hydrophobically-modified silica, 87.3 parts of 10,000 cstks silicone oil, and 10 parts of polysiloxaneoxyalkylene block copolymer surfactant. Because of lower surface tension, the silicone antifoams tend to be more effective than the hydrocarbon antifoam; they are, however, more costly.
The mechanism of defoaming is not yet understood completely. This is particularly true in the case of antifoams utilizing hydrophobic oil and hydrophobic particles. However, in Chem. Eng. Prog. 63(9) (1967), Ross has proposed two simple mechanisms for antifoams which do not have hydrophobic particles. In the first mechanism, an antifoam droplet enters the film between two bubbles and spreads as a thick duplex film; the spreading action sets up tensions that mechanically break the foam. According to the second mechanism, the antifoam droplet enters the liquid film but only spreads to a limited extent, producing a mixed monolayer with the foam agent. If this mixed monolayer has poor coherence, the foam will be broken.
Kulkarni et al. have proposed in Ind. Eng. Chem. Fundam. 16, 472 (1977), that in systems of silicone oil and hydrophobic silica particles the real foam breakers are the silica particles. They reason that the silicone oil brings the particles to the interface between the air and bubble film by spreading them over the film surface. The silica particles adsorb surfactant, resulting in local depletion of surfactant at the bubble surface, causing bubble shock and instability. On the other hand, P. R. Garrett has proposed in J. Colloid and Interface Science 1980, 76, 587 that silicone oil is the real foam breaker; the silicone oil droplets bridge thin liquid foam films and are subsequently drawn apart by capillary forces to form a hole resulting in film rupture. Under this theory, the hydrophobic particles sit at the interface of oil and water (film), facilitating the formation of the oil bridges and, therefore, the rupture of foam films.
The presence of antifoam agents in laundry detergent compositions is particularly important under washing conditions wherein the surfactant concentration in washing machines is high such that the foam problem is severe, unless an antifoam agent is included in the formulation. A successful foam control will allow higher active (surfactant) content and freedom to choose surfactants in detergent formulation. Use of antifoams desirably results in products of better performance and lower cost. To achieve such results, one might attempt to switch from a hydrocarbon based-antifoam to a mixture of hydrocarbon and silicone antifoams. However, the antifoaming performance of such mixtures exceeds that of the pure hydrocarbon antifoams but is still below that of the silicone-based antifoams. The present invention pertains to an antifoam which offers performance comparable to the silicone antifoams with a cost comparable to a mixture of hydrocarbon and silicone.
It is known in the art from, e.g., Encyclopedia of Chemical Technology, Vol. 7, pp. 430-447 (1979) that inorganic fillers such as silica particles increase the antifoam efficiency. The use of hydrophilic silica such as precipitated and fumed silica in silicone-based antifoam is disclosed in U.S. Pat. Nos. 3,560,401, 4,076,648, and 4,101,443. The procedure used therein generally involves heating the silica particles and silicone oils together at 100.degree. C. to 150.degree. C. for several hours to complete the hydrophobization of the silica particles and to fluidize the mixture.
To avoid this time-consuming and cumbersome hydrophobing step, hydrophobic silica particles have been used. These are disclosed in U.S. Pat. No. 4,395,352 for silicone-based antifoams and in U.S. Pat. Nos. 3,076,768; 3,388,073 and 3,714,068 for hydrocarbon-based antifoams.
O'Hara et al., U.S. Pat. No. 3,560,403 discloses the use of certain reactive alkylaminosilicones to hydrophobe silicate particles in situ in a process for making antifoam compositions. The alkylaminosilicone compounds used therein are represented by the formula (R.sub.2 N).sub.x (SiR.sub.2 O).sub.m SiR.sub.2 (R).sub.2-x. An example is (Me.sub.2 N)(SiMe.sub.2 O).sub.20 SiMe.sub.3. A chemical reaction between the silicate silanols and the dialkylamino organosilicone fluid is said to take place releasing dimethylamine and resulting in a hydrophobic surface on the silicate particles. The reaction is said to take place without the necessity of heating and cooling cycles. The alkylaminosilicones of O'Hara et al. are quite different from those of the present invention; their nitrogen atoms attach directly to the silicon atom whereas the compounds of our invention have at least three carbon atoms separating the nitrogen and silicon atoms. The alkylaminosilicones of the present invention are not chemically reactive toward silanols. The antifoams are said to be useful in laundry and detergent products, among other applications.
Griswold et al., U.S. Pat. No. 4,584,125 discloses an antifoam composition including a non-aqueous liquid such as a diorganopolysiloxane or mineral oil, an amine-containing compound selected from an aminofunctional organopolysiloxane and/or an organic amine, and an inorganic filler. The amino-functional organopolysiloxane may be of the formula ##STR1## wherein R.sup.3 may be a divalent hydrocarbon or hydrocarbonoxy radical. Tertiary amino organosilanes or siloxanes which have at least one ether linkage in the organic group connecting the tertiary amino group to the silicon atoms may also be used. It is said that the Griswold et al. antifoam can be prepared at room temperature and at atmospheric pressure. The compositions are said to be useful in laundry and detergent products.
Morehouse U.S. Pat. No. 3,032,577 discloses organosiloxanes which are said to be useful for a variety of applications in the synthetic polymer art, particularly as flocculating agents for aqueous dispersions of clay. The organosiloxanes of the Morehouse patent include units of the formula: ##STR2## wherein --OZ-- is the divalent group derived from a monoepoxide by opening of the oxirane ring, HO is interconnected to N through 2 carbon atoms, a is an integer from 0 to 1, n is an integer from 3 to 15, and R may be hydrogen, monovalent hydrocarbon or ##STR3## Z may be a hydrocarbon-substituted ethylene such as ##STR4## The Morehouse compounds are said also to be useful as complexing agents for removing metal ions, particularly cupric and ferric ions.
Kulkarni et al., U.S. Pat. No. 4,514,319 discloses antifoam compositions comprising a hydrocarbon-silicone copolymer in combination with a hydrocarbon carrier oil, an organosilicone surfactant, a hydrophobic filler and optionally a silicone oil. Although the composition is said to work as an efficient antifoam, it appears not to have self-hydrophobing properties in that it appears necessary to use hydrophobic silica particles or to heat the mixture with hydrophilic silica particles.